Question

The heat of neutralisation of 1 mole of ${HClO}_4$ with 1 gm-equivalent of NaOH in aqueous solutions isX kJ ${mol}^{-1}$ .Find out value of X

• A. $X=-57.2$
• B. $X=+57.2$
• C. $X=-47.2$
• D. None of these

Answer 1

Answer: (A)

$X=-57.2$

The equation for any strong acid being neutralised by a strong alkali is essentially just a reaction between hydrogen ions and hydroxide ions to make water. The other ions present (sodium and perchlorate for example) are just spectator ions, taking no part in the reaction.

$NaOH+HCl{O}_4⟶NaCl+H_{2}O$

. . . but what is actually happening is:

$H^{+}+{OH}^{-}⟶H_{2}O$

If the reaction is the same in each case of a strong acid and a strong alkali, it isn't surprising that the enthalpy change is similar.

So the heat of neutralisation will be $=-57.2KJ/mol$, constant for all strong acid and base.